In the manipulation of machinery, particularly farm implements, it is often necessary to hydraulically raise and lower the machinery repeatedly and reliably to preset positions. In the case of farm equipment, for example, it may be necessary for a tractor operator to lower a plow or other implement to a particular postion so as to plow land to a desired depth. This depth may change according to varying requirements and it is therefore necessary that the operator have the ability to change this depth with ease. Furthermore, it may be necessary to frequently raise the implement off the ground for maintenance, or the like, and then return the implement to the proper depth setting.
In the prior art, systems have been developed employing hydraulic cylinders with variable position pistons which serve as stroke limiters for the hydraulic cylinder. In these prior art systems, the position of the stop piston is controlled by adjustable valves. Typically, however, these valving systems are not absolutely fluid-tight and the stop piston may tend to drift from its original preset location. As a result, the tractor operator, for example, will need to reset the depth of the implement many times to ensure uniformity. In addition, these systems lack means for disconnecting the implement from the power source (tractor) while maintaining their preset position and relieving pressure in the couplings for easy disconnection.
Furthermore, this resetting requirement is complicated by the fact that prior art devices lack simple visual means for checking the actual position of the piston, and in turn the relative position of the implement. The present invention discloses a solution to the problem of fluid leakage and the resultant unreliability while independently providing a simple visual indicator which precisely indicates the relative position of the implement to ensure uniformity.